ZyXEL VES1724-56B2 User Guide - Page 218
IGMP Snooping and VLANs, IGMP Proxy, Multicast Listener Discovery, MLD Messages
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Chapter 24 Multicast 24.1.4 IGMP Snooping and VLANs The Switch can perform IGMP snooping on up to 16 VLANs. You can configure the Switch to automatically learn multicast group membership of any VLANs. The Switch then performs IGMP snooping on the first 16 VLANs that send IGMP packets. This is referred to as auto mode. Alternatively, you can specify the VLANs that IGMP snooping should be performed on. This is referred to as fixed mode. In fixed mode the Switch does not learn multicast group membership of any VLANs other than those explicitly added as an IGMP snooping VLAN. 24.1.5 IGMP Proxy IGMP proxy enables a layer-2 switch to maintain a joined member list for each IGMP group on the switch. This switch automatically and periodically sends queries to the VDSL ports to get the subscribing information and response the upper layer router's query for the member list. In addition, it enables the switch not to report the leave request sent from one subscriber to upper layer router if there are still other subscriber(s) in the same IGMP group. It also allows the switch not to report the join request sent from one subscriber to upper layer router if any subscriber is still in the same IGMP group. In other words, an IGMP proxy switch only forward the first join request and the last leave request in an IGMP network to its upper layer router. It can reduce multicast traffic significantly. Note: Note: You must set one of Gigabit Ethernet ports to "Fixed mode" before enabling IGMP proxy. 24.1.6 Multicast Listener Discovery The Multicast Listener Discovery (MLD) protocol (defined in RFC 2710) is derived from IPv4's Internet Group Management Protocol version 2 (IGMPv2). MLD uses ICMPv6 message types, rather than IGMP message types. MLDv1 is equivalent to IGMPv2 and MLDv2 is equivalent to IGMPv3. MLD allows an IPv6 switch or router to discover the presence of MLD hosts who wish to receive multicast packets and the IP addresses of multicast groups the hosts want to join on its network. MLD snooping and MLD proxy are analogous to IGMP snooping and IGMP proxy in IPv4. MLD filtering controls which multicast groups a port can join. 24.1.7 MLD Messages A multicast router or switch periodically sends general queries to MLD hosts to update the multicast forwarding table. When an MLD host wants to join a multicast group, it sends an MLD Report message for that address. An MLD Done message is equivalent to an IGMP Leave message. When an MLD host wants to leave a multicast group, it can send a Done message to the router or switch. If the leave mode is not set to immediate, the router or switch sends a group-specific query to the port on which the Done message is received to determine if other devices connected to this port should remain in the group. 218 VES1724-56 User's Guide